“The world is spinning around in a circle!” If you spin around, you get dizzy. That’s not exactly rocket science. We’ve all been there. But you can hijack your senses like we just
did and get what I’m gonna call weird dizzy. And it can teach us how our bodies know where
they are in space. Hey smart people, Joe here. How do you know when your body is moving? For most of us, the answer is right here. We can see ourselves moving. Ok, but what if you’re blindfolded? You have a special sense that tells you whether
your body is moving and how your body is oriented in three dimensions. It’s called your vestibular sense. And if you spin around in circles, you can
break it. But it turns out you can break your vestibular
sense system in a few different ways, if you change how you get dizzy. We’re gonna do a little experiment, to see
if maybe we can decode how this vestibular sense works. Of course, I’m not gonna get dizzy. I’m gonna make my friend Vanessa Hill from
Braincraft do it. Every experiment needs a control group… Hello, hello. Hi, it's great to be here. Yeah, I'm kind of excited. When you were a kid did you ever sit down in an office chair and spin yourself around as fast as you could? Definitely Ok, have you ever done it when you were an adult? No. Your sitting in an office chair, surprise. Are you ready? I guess so. She's not ready How do you feel? Ok, everything's moving back and forth like this. So that’s normal dizzy. Most of us have felt that. Not too bad. Well, watch this. We're going to do this again, but this time we're going to hold your head in a different position Ok you head, you know eyeballs down 90 degrees or you can look straight up So if I throw up it will either be back on my back or just on my lap Probably safer to throw up down Ok, I'm going to do that then The world is spinning around in a circle, but it was like on an arc, everything was going up and down What other way is there? You're going to hold your head to the side so that your ear is facing the floor Ready? I suppose! OH MY GOD Oh that is horrible! The whole world is just moving up and down, ok so there's a light right here so the light was moving like this, just continually up and down Ok, so what the heck is going on? Your vestibular system is located in your
inner ear. It has two important parts: the semicircular
canals, and the otoliths. “Otolith” means “ear stone”. They are literally little chunks of calcium
carbonate suspended inside your head. Basically every vertebrate has them, from
fish to birds to mammals, and they’re how we sense gravity and know which way is up
or down. Otoliths also sense linear motion. For our dizzy experiment though, we’re interested
in rotational motion, not linear motion. And rotational motion is sensed by the semicircular
canals. The semicircular canals are tubes in the shape
of half circles, and inside, they’re filled with fluid. There are 3 semicircular canals in each inner
ear -- three on the left and 3 on the right, for 6 total. Having three canals allows your body to sense
motion in three dimensions, along three planes at perpendicular angles to each other. The superior canal detects movement
along the x-axis The lateral canal detects movement along the
y-axis And the posterior canal detects movement on
the z-axis Your inner ears are basically like the inertial
guidance system in an airplane, which tells the pilot about the plane’s pitch, yaw,
and roll. How do they do that? They use PHYSICS! Sigh… but doesn’t everything? Specifically, they use inertia, an object’s
resistance to a change in its motion. Now, when your skull moves, the liquid in
your semicircular canal doesn’t move immediately with it; it sloshes around inside its tube. The semicircular canals have special cells
that sense motion called hair cells. That inertia sloshing bends the hair cells,
and bending causes a change in the signals fired to the brain. The hair cells are actually firing all the
time, even when you’re sitting still, but bending in one direction increases the rate
of firing, and bending in the other direction decreases the rate of firing. Each pair of canals, right and left, work
together, and your brain adds up their signals in a way that not only says “your head is
moving” but tells you in which direction! Vanessa held her head in different axes–
x, y, and z–while spinning, which sloshed the liquid in each of her three semicircular
canals, one for each axis of motion, which gave three different sensations of dizziness. Did you notice when Vanessa said the room
looked like it was spinning? You’ve probably experienced that when you
were dizzy too. Well, the room wasn’t spinning, I checked. I had her hold a camera up to her eyes right
as she stopped moving. Watch what happened. When you get dizzy, your eyes respond by jumping
back and forth involuntarily. It’s called nystagmus. If you look very closely, you’ll see Vanessa’s
eye movements are actually faster in one direction and slower in the other. Normally, if you move your head with your
eyes open, a reflex called the vestibulo-ocular response moves your eyes in the opposite direction
of your head’s motion, in order to keep your eyes fixated on a target. Have you ever watched a dancer spin, and noticed
how they spot on something and move their head and eyes opposite of the spin? It’s like that. When you stop spinning suddenly, your eye keeps twitching in the opposite direction of spin. It’s a reflex. The reason the room looks like it’s spinning
when YOU stop is because your eye movements are MAKING it spin. When Vanessa held her head in different positions, the room seemed to spin in different directions! Because her vestibulo-ocular response reacted in three different ways So how do figure skaters, pilots, or sk8r
bois not get dizzy if they do so much spinning? They do a lot of practice, and their bodies
adapt. For most sensations or feelings our bodies
experience, when they’re repeated and repeated, the body’s response gets weaker, it sort
of tunes down the volume. You’ve probably experienced this getting
into cold or hot water, at first your body REALLY senses it, but that response gets weaker
as our brain tunes it down, even though you’re still feeling the cold or the heat. It becomes your new normal. If we consciously felt everything we’re
feeling all the time, it would be total sensory overload. And when figure skaters, pilots, or sk8r bois
practice spinning over and over, their short-term dizziness response gets weaker and weaker. Because we evolved on Earth, these vestibular
senses rely a lot on gravity. Up in a micro-zero g environment like the
Space Station, astronauts and their inner ears are constantly falling together, all
the time. So an astronaut’s vestibular system adapts
to this new normal after just a few days up there So I wanted to do a quick check today and just to see if I can make myself dizzy it's not making me feel ill at all, not in the slightest not dizzy Down here on Earth, some people’s vestibular
systems don’t work the right way, and they can give sensations of movement or falling
even when that’s not happening. That’s called vertigo. And it can make life pretty uncomfortable. If you want to try this at home, it's super fun, you should just make sure to do it with a friend, or to a friend, and wear a helmet We didn't wear a helmet did we? And you know that funny feeling in your head right now? That's called learning. Could be dizziness too. Stay curious.
